Gram-Positive Cocci Overview

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Questions and Answers

What is the cellular arrangement of Staphylococci?

  • Pairs
  • Grape-like clusters (correct)
  • Chains
  • Single cells

Which of the following is a coagulase positive Staphylococcus?

  • Staphylococcus aureus (correct)
  • Staphylococcus hominis
  • Staphylococcus epidermidis
  • Staphylococcus saprophyticus

What enzyme does Staphylococcus aureus produce that is significant for clot formation?

  • Lipase
  • Protease
  • Hyaluronidase
  • Coagulase (correct)

Which of the following is NOT a characteristic of Staphylococcus aureus?

<p>Motile (B)</p> Signup and view all the answers

What is the significance of teichoic acid found in Staphylococcus aureus?

<p>Involved in attachment and may cause septic shock (B)</p> Signup and view all the answers

How is Staphylococcus aureus primarily transmitted?

<p>Hand contact (B)</p> Signup and view all the answers

What distinguishes Methicillin-resistant Staphylococcus aureus (MRSA) strains?

<p>Antibiotic resistance (A)</p> Signup and view all the answers

Which virulence factor is associated with causing wound infections by Staphylococcus aureus?

<p>Collagen-binding proteins (C)</p> Signup and view all the answers

What is the primary cause of Scalded Skin Syndrome caused by Staphylococcus aureus?

<p>Production of exfoliative toxins (D)</p> Signup and view all the answers

Which of the following symptoms is NOT typical of septic shock?

<p>Rash (B)</p> Signup and view all the answers

What characterizes the systemic infections caused by Staphylococcus aureus?

<p>Seeding of various tissues through the bloodstream (B)</p> Signup and view all the answers

Which toxin is specifically associated with food poisoning due to Staphylococcus aureus?

<p>Enterotoxin B (B)</p> Signup and view all the answers

Which of the following infections is NOT caused by Staphylococcus aureus?

<p>Tetanus (C)</p> Signup and view all the answers

What is a major consequence of the cytokine production induced by Enterotoxin B?

<p>Stimulation of the vomiting center (A)</p> Signup and view all the answers

Which of the following conditions is associated with high fever and subsequent circulatory collapse?

<p>Septic shock (D)</p> Signup and view all the answers

Which of the following is a characteristic of non-pyogenic skin infections caused by Staphylococcus aureus?

<p>Includes cellulitis and impetigo (D)</p> Signup and view all the answers

What is a primary clinical concern associated with Staphylococcus epidermidis?

<p>Infecting intravenous catheters and prosthetic implants (B)</p> Signup and view all the answers

Which characteristic is NOT true for streptococci?

<p>They are catalase-positive (D)</p> Signup and view all the answers

Which group of streptococci produces a clear zone around their colonies on blood agar?

<p>Beta-hemolytic streptococci (D)</p> Signup and view all the answers

What type of infections is Staphylococcus saprophyticus primarily known for causing?

<p>Urinary tract infections in sexually-active young women (A)</p> Signup and view all the answers

What is the primary pathogen among the Streptococci species?

<p>Streptococcus pyogenes (A)</p> Signup and view all the answers

What is the method of classification for beta-hemolytic streptococci that is based on carbohydrate antigens?

<p>Lancefield grouping (A)</p> Signup and view all the answers

Which condition is often associated with Streptococcus pyogenes due to the production of erythrogenic toxin?

<p>Scarlet Fever (D)</p> Signup and view all the answers

Which characteristic differentiates gamma-hemolytic streptococci from alpha and beta types?

<p>They do not produce any hemolysis. (A)</p> Signup and view all the answers

What inflammation is primarily caused by Streptococcus pyogenes, especially among children?

<p>Pharyngitis (C)</p> Signup and view all the answers

Which bacterium is a major cause of sepsis in neonates?

<p>Staphylococcus epidermidis (D)</p> Signup and view all the answers

What role does Streptokinase play in medical treatment?

<p>It dissolves fibrin in clots. (D)</p> Signup and view all the answers

What is the primary mechanism of hemolysis for beta-hemolytic streptococci?

<p>Complete lysis of red blood cells by exotoxins (B)</p> Signup and view all the answers

What is a characteristic feature of necrotizing fasciitis caused by certain strains of Streptococcus pyogenes?

<p>Massive tissue necrosis (C)</p> Signup and view all the answers

Which of the following is a common inhabitant of the human microbiota that can cause infections?

<p>Streptococcus agalactiae (C)</p> Signup and view all the answers

What disease can arise from a throat infection with Streptococcus pyogenes?

<p>Bacteremia (D)</p> Signup and view all the answers

What is the mode of transmission for Streptococcus pyogenes?

<p>Respiratory aerosols (C)</p> Signup and view all the answers

What severe condition may result from the rapid spread of Streptococcus pyogenes in the body?

<p>Sepsis and septic shock (C)</p> Signup and view all the answers

What is the primary cause of Puerperal Sepsis?

<p>Streptococcus pyogenes (D)</p> Signup and view all the answers

Which of the following complications is characterized by damage to heart valves due to autoimmune responses?

<p>Acute rheumatic fever (C)</p> Signup and view all the answers

Which organism is associated with nephritogenic strains responsible for Acute Glomerulonephritis?

<p>Streptococcus pyogenes (C)</p> Signup and view all the answers

What treatment or intervention is most critical for managing the complications sequential to a Streptococcal infection?

<p>Immediate antibiotic therapy (D)</p> Signup and view all the answers

What symptom is NOT commonly associated with Acute Glomerulonephritis?

<p>Chest pain (A)</p> Signup and view all the answers

What type of antibodies are formed due to cross-reacting human antigens after Streptococcus pyogenes infection?

<p>Cross-reacting auto-antibodies (A)</p> Signup and view all the answers

How long after a streptococcal infection can Acute Glomerulonephritis develop?

<p>1-3 weeks after recovery (A)</p> Signup and view all the answers

Flashcards

Staphylococci arrangement

Grape-like clusters of spherical, gram-positive cocci.

Streptococci arrangement

Chains of spherical, gram-positive cocci.

Staphylococcus aureus

A medically important type of staphylococcus commonly found (30-50%) in human nose, also in vaginal tract, known for various virulence factors.

Coagulase-positive staphylococci

Staphylococcus species that produce coagulase enzyme, an important virulence factor that causes plasma clotting.

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Coagulase-negative staphylococci

Staphylococcus species that do not produce coagulase.

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Teichoic acid

A virulence factor found in Staphylococcus aureus that helps with attachment and septic shock.

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MRSA

Methicillin-resistant Staphylococcus aureus, a strain of Staphylococcus aureus resistant to certain antibiotics.

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Virulence factor examples

Examples of virulence factors include teichoic acid, collagen binding proteins, toxins, that promote infection and harm.

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Scalded skin syndrome

A skin condition caused by toxins produced by certain strains of Staphylococcus aureus, leading to blistering and peeling of the skin.

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Exfoliative toxins

Toxins produced by some S. aureus strains that break down the bonds between skin layers, causing peeling.

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Enterotoxin B

A heat-stable toxin produced by some S. aureus strains that causes food poisoning, leading to vomiting and diarrhea.

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What causes staphylococcal food poisoning?

Ingestion of food contaminated with Staphylococcus aureus strains producing enterotoxin B, a heat-stable toxin.

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Septic shock from S. aureus

Life-threatening condition caused by S. aureus infection spreading into the bloodstream (septicemia), triggering widespread inflammation and organ damage.

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How does S. aureus cause internal infections?

From major abscesses, S. aureus enters the bloodstream (septicemia) and spreads to various organs causing internal infections and potentially septic shock.

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What does S. aureus cause?

S. aureus can cause a range of infections from localized skin infections like boils to serious systemic infections including septicemia and endocarditis.

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What are the symptoms of septic shock?

Initially: High fever and rapid heart rate. Later: Decrease in body temperature, blood clots (disseminated intravascular thrombosis), bleeding, low blood pressure, organ failure, coma, and death.

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Streptococcus pyogenes

A bacterial species that causes various infections, including strep throat, scarlet fever, and necrotizing fasciitis.

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Strep throat

A common throat infection caused by Streptococcus pyogenes, characterized by sore throat, swollen tonsils, and sometimes fever.

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Scarlet fever

A complication of Strep throat caused by Streptococcus pyogenes producing an erythrogenic toxin. It is characterized by a distinctive rash and strawberry-colored tongue.

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Necrotizing fasciitis

A severe skin infection caused by certain strains of Streptococcus pyogenes, characterized by rapid tissue death and necrosis.

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Streptokinase

An enzyme produced by Streptococcus pyogenes that dissolves fibrin clots.

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Exotoxin B

A cysteine protease toxin produced by Streptococcus pyogenes that contributes to necrotizing fasciitis.

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Endogenous infection

An infection caused by bacteria that are already present in the body's normal microbiota.

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Pyogenic inflammation

Inflammation characterized by the production of pus.

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What are the primary causes of Staph epidermidis infections?

Staphylococcus epidermidis is a common skin flora, but it's notorious for causing infections in implanted medical devices, like catheters, heart valves, and prosthetic joints. It also contributes to sepsis in newborns and peritonitis in dialysis patients.

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Why is Staphylococcus saprophyticus important in young women?

Staphylococcus saprophyticus is a major cause of urinary tract infections, especially in sexually active young women.

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Describe the arrangement of Streptococci.

Streptococci are spherical, Gram-positive bacteria that arrange themselves in chains.

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Catalase reaction for Streptococci.

Streptococci are catalase-negative, meaning they don't produce the enzyme catalase to break down hydrogen peroxide.

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Alpha hemolytic Streptococci

Alpha hemolytic streptococci produce a green zone around their colonies on blood agar due to the reduction of hemoglobin to methemoglobin by hydrogen peroxide.

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What is the effect of Beta-hemolytic Streptococci on red blood cells?

Beta-hemolytic Streptococci completely lyse red blood cells, forming a clear zone around their colonies on blood agar. This lysis is caused by hemolysin toxins, which create pores in cell membranes.

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Gamma Hemolytic Streptococci

These are non-hemolytic species of Streptococci. They don't cause any change in the blood agar around their colonies.

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Lancefield Grouping

This grouping system classifies most Beta-hemolytic Streptococci based on a particular type of carbohydrate antigen (C carbohydrate) found on their cell walls.

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Erysipelas

A skin infection caused by Streptococcus pyogenes affecting the dermal layer. It leads to redness, swelling, and pain.

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Puerperal Sepsis

A serious infection affecting mothers after childbirth, caused by Streptococcus pyogenes. It starts in the uterus and can spread to the abdominal cavity, leading to peritonitis.

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Post-Streptococcal Diseases

Conditions that develop after Streptococcus pyogenes infection, triggered by the body's immune response. These include Acute Glomerulonephritis and Rheumatic Fever.

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Acute Glomerulonephritis

Inflammation of the glomeruli in the kidneys, often following a Streptococcus pyogenes infection. It causes blood and protein in the urine, swelling, and high blood pressure.

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Acute Rheumatic Fever

An autoimmune complication of a Streptococcus pyogenes infection that affects the heart. It causes damage to the heart valves and surrounding tissues.

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What are the most common types of nephritogenic M strains?

The most common types of nephritogenic M strains are types 12 and 49. They are responsible for causing Acute Glomerulonephritis.

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Antibodies in Acute Glomerulonephritis

Antibodies formed against Streptococcus pyogenes antigens can bind to human antigens, causing deposits of immunocomplexes on the glomerular capillaries.

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Study Notes

Gram-Positive Cocci

  • Gram-positive cocci are spherical bacteria arranged in characteristic patterns
  • Gram-positive cocci can be divided into staphylococci and streptococci
  • Staphylococci form grape-like clusters while streptococci form chains

Staphylococci

  • General features: spherical, Gram-positive, arranged in grape-like clusters, catalase-positive, non-motile, facultative anaerobic bacteria
  • Medically important species include Staphylococcus aureus (most important), Staphylococcus epidermidis and Staphylococcus saprophyticus
  • Classification based on coagulase enzyme: coagulase-positive (produce coagulase) and coagulase negative (do not produce coagulase)
    • Staphylococcus aureus is the example of coagulase-positive
    • Staphylococcus epidermidis and Staphylococcus saprophyticus are examples of coagulase-negative species
  • Coagulase: enzyme inducing plasma coagulation by activating prothrombin to thrombin and then fibrin
  • important virulence factors: Teichoic acid, Collagen-binding proteins (in attachment), and different exotoxins (proteases like collagenase and elastase, lipases, hyaluronidase, Pore-forming toxins like PV Leukocidin, Toxic Shock Syndrome Toxin (TSST), Exfoliative toxin(scalded skin syndrome) , Enterotoxin B)

Staphylococcal Infections

  • Local skin infections (tissue destruction and pus formation): folliculitis, boils, wound infections, furuncles, carbuncles
  • Systemic infections (reach the blood stream): septicemia, endocarditis, osteomyelitis, meningitis, pneumonia, septic shock
  • Septic shock can be caused by Teichoic acid or TSST.

Staphylococcus aureus

  • Epidemiology/Transmission: 30-50% of people carry in anterior nares, 5% in vaginas, spreading possible via hands, skin, throat and other surfaces
  • MRSA (Methicillin Resistant Staphylococcus aureus) common, VRSA appeared
  • important virulence factors: Teichoic acid, Collagen-binding proteins, Exotoxins and Exfoliative Toxin: involved in scalded skin syndrome and causes tissue damage, and Enterotoxin B involved in food poisoning.

Other diseases caused by S. aureus

  • Non-pyogenic skin conditions: cellulitis and impetigo
  • Scalded skin syndrome(SST): epidermolytic toxins (exfoliative toxins) cleave desmogleins in superficial skin layers causing massive skin exfoliation; fever, large areas of skin slough, secondary infections, electrolyte imbalances can occur

Staphylococcal Food Poisoning

  • Ingestion of food heavily contaminated with S. aureus strains containing enterotoxin B can result in self-limiting vomiting and watery diarrhea.
  • Enterotoxin B: a super-antigen that induces cytokine production in mesenteric lymph nodes after food ingestion
  • Cytokines stimulate vomiting center in the brain

Staphylococcus epidermidis and Staphylococcus saprophyticus

  • Both coagulase-negative staphylococci
  • S. epidermidis is part of the normal human skin flora (90% of normal skin microbiota) found on skin and mucous membranes
  • It commonly infects intravenous catheters and prosthetic implants (e.g. prosthetic heart valves, vascular grafts, prosthetic joints (arthritis or osteomyelitis)
  • It can cause sepsis in neonates and peritonitis in patients with renal failure on peritoneal dialysis
  • S. saprophyticus causes urinary tract infections, especially in sexually active young women

Streptococcus

  • Spherical, Gram-positive cocci that form chains
  • Catalase-negative
  • Are non-motile
  • Facultative anaerobes
  • Classified based on hemolytic activity: Alpha-hemolytic, Beta-hemolytic, Gamma-hemolytic
    • Alpha-hemolytic: green zone around colonies due to hemoglobin reduction to methemoglobin
    • Beta-hemolytic: clear zone around colonies due to complete lysis of red blood cells
    • Gamma-hemolytic: no change around colonies
  • Classification based on Lancefield Grouping: important CHO antigen of the cell wall (e.g. C carbohydrate)

Streptococcus pyogenes (Beta-hemolytic/Group A)

  • Key pathogen
  • Commonly found in skin and throat
  • Important virulence factors: M protein (anti-phagocytic), capsule (anti-phagocytic, surface disguise), Teichoic acid(can cause toxic shock), Pore-forming toxins (hemolysins like Streptolysin), Pyogenic exotoxin A, (super-antigen, causing toxic shock)
  • Infections: Pharyngitis (strep throat), scarlet fever (rash, strawberry tongue), Otitis media, bronchitits, pneumonia (bacteremia, septic shock), meningitis, non-pyogenic skin infections (cellulitis and impetigo), toxic shock (systemic disease), Streptococcal gangrene (necrotizing fasciitis), Erysipelas, Puerperal sepsis (childbirth fever)
  • Post-Streptococcal diseases: Acute glomerulonephritis, acute rheumatic fever (immune reaction against streptococcal M protein), subcutaneous nodules, Sydenham’s chorea

Post-Streptococcal diseases

  • Acute glomerulonephritis: inflammatory condition affecting glomeruli (kidneys) due to cross-reacting antibodies binding to human antigens
  • Acute rheumatic fever: inflammation of heart valves caused by immune response to streptococcal M protein and other antigens causing heart valve damage

Other Streptococcus

  • Viridans streptococci: commonly found in the oropharynx
  • Streptococcus agalactiae: found in vagina and colon
  • Enterococci and anaerobic streptococci: found in the colon

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